1. Field
The present disclosure relates generally to the field of image processing, and more specifically to an auto-focus technique in image capture devices such as still picture cameras and video cameras.
2. Related Art
An image capture device (ICD) generally refers to a device which captures images of scenes. When designed to capture a single image of a scene, the device is referred to as a camera. On the other hand, when continuous images of a scene are captured by a device, the device is often referred to as a camcorder. The images can be captured in digital form or analog form. To capture images in digital form, sensors may be arranged in the form of an array, with each sensor in the array forming a digital value representing a point (small portion) of the scene. On the other hand, in analog form, a light-sensitive medium is designed to respond to incident rays to capture the image. In general, the sensors and other media which capture the images are referred to as capturing media.
ICDs also generally contain a lens assembly, which receives light rays representing a scene sought to be captured, and converges the light onto the capturing medium. The lens assembly may contain one or more lenses, which can be configured to obtain various degrees of convergence. In one embodiment, configuration entails moving the absolute and/or relative position of individual lenses (typically along an imaginary axis connecting the lens assembly to the capturing medium) contained in a lens assembly. However, configuration can entail any other changes (e.g., effecting curvature change, etc.) as provided by the present/future underlying technology to effect focusing (described below) of the received light rays to the capturing media.
It is generally required to focus on a scene of interest before capturing the scene. Focusing refers to configuring a lens assembly such that the incident light rays are made to converge on the capturing medium. As a simplified illustration, it may be appreciated that parallel light rays originating at infinite distance would be received in parallel and would converge at a distance equaling a focal length of the lens assembly.
As a scene gets closer, the rays may be less than parallel (i.e., divergent), and thus the distance between the lens assembly and the capturing medium may need to be correspondingly more than the focal length (assuming the focal length of the lens assembly does not change). In general, a resulting captured image is rendered distinct and clear when the focusing is accurate. When the lens assembly is focused less than accurately, the clarity of the captured image is generally correspondingly less.
Several ICDs provide a manual mechanism by which a user can configure lens assembly to obtain a desired focus, typically while viewing the image through the lens assembly. Assuming only the position of the lens needs to be adjusted for focusing, the lens position is changed directly in response to the user operation of the manual mechanism. Once a desired focusing is set, the user then captures the image. Such manual mechanism to configuring lens assembly may be termed as manual focusing.
On the other hand, there has been a general recognized need for auto-focus ICDs. Auto-focusing generally refers to determining the appropriate parameters (e.g., distance in the examples above) to configure the lens assembly, and performing the determined configuration by using appropriate computations and configurations within an ICD.
In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.